JPH0371662B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Background of the Invention (Field of Industrial Application) The present invention relates to a bicarbonate ion sensor, more particularly a solid-state bicarbonate ion sensor without an internal (standard) solution, and more preferably a solid-state bicarbonate ion sensor without an internal (standard) solution. , relates to a bicarbonate ion sensor that can also be measured in living organisms. (Prior Art and its Problems) The concentration of bicarbonate ions has a deep correlation with the respiratory and metabolic functions of living organisms, and is often examined for the purpose of adjusting and monitoring the electrolyte balance of living organisms. Conventionally, a hydrogen carbonate ion sensor that measures the hydrogen carbonate ion concentration in a solution using electrode potential response and can be miniaturized in a solid state has been developed by depositing a redox film on a conductive substrate and then adding a hydrogen carbonate ion carrier film. There is a deposited electrode potential responsive bicarbonate ion sensor. However, since the electrode consisted of a conductive substrate/redox membrane/bicarbonate ion selective membrane,
There was a drawback that the properties of the electrode for dissolving the redox membrane composition into the bicarbonate ion-selective membrane or the dissolution of the bicarbonate ion-selective composition into the redox membrane were impaired in about one month. Purpose of the Invention Therefore, the present invention provides a method for selecting interfering ions, in which mutual dissolution and elution of the substance constituting the redox functional layer and the substance constituting the hydrogen carbonate ion selective layer do not occur, the ionic characteristics are stable for a long period of time, and the ionic properties are stable for a long period of time. The purpose of the present invention is to provide a bicarbonate ion sensor with high performance and fast ion response speed. The above object is to provide a bicarbonate ion sensor that includes an ion-sensing section and measures the ion concentration in a solution by electrode potential response, wherein the ion-sensing section has a conductive substrate and a redox function that covers the surface of the conductive substrate. a partition layer covering the surface of the redox functional layer, and a bicarbonate ion selective layer covering the surface of the partition layer, the partition layer comprising the bicarbonate ion selective layer and the redox functional layer. It has the function of preventing the movement of substances constituting each layer between the layers and transmitting the potential difference generated in the bicarbonate ion-selective layer from the bicarbonate ion-selective layer to the redox functional layer due to contact with bicarbonate ions. This is achieved by a bicarbonate ion sensor characterized by having. DETAILED DESCRIPTION OF THE INVENTION The present invention will be specifically described below based on examples. The features of the present invention can be clearly understood by referring to FIG. 1 and Tables 1 and 2. FIG. 1 is a block diagram of an embodiment of an ion sensor according to the present invention. Conductive substrate/(diameter 1.1mm
A lead wire 2 made of a Teflon-coated copper wire (0.2 mmφ) is fixed to the bottom surface 1a of the body (length 3.0 mm) with a conductive adhesive 8, and an insulating layer 9 is formed so that the conductive substrate 1 is exposed by 1.5 mm. Furthermore, the outer periphery is covered and insulated with a heat shrink tube 4. Furthermore, the exposed tip of the conductive substrate 1 was polished into a hemispherical shape, and the surface area of the exposed portion was adjusted to 0.061 cm ² (average).
A redox functional layer 5 is formed on the exposed surface of the conductive substrate 1 by electrolytic oxidative polymerization. The conductive substrate 1 used in the bicarbonate ion sensor of the present invention is, for example, basal platen pyrolitex graphite (basal platen pyrolitex graphite).
plane pyrolytic graphite (hereinafter referred to as BPG),
Conductive carbon materials such as glassy carbon; metals such as gold, platinum, copper, silver, palladium, nickel, and iron, especially noble metals, or those whose surfaces are coated with semiconductors such as indium oxide and tin oxide. It will be done. Among these, conductive carbon materials are preferred;
BPG is particularly preferred, and the shape is preferably cylindrical. In addition, the layer 5 having a redox function (hereinafter sometimes referred to as a redox functional layer) means that an electrode formed by depositing this layer on the surface of a conductive substrate is applied to the conductive substrate at a constant potential by a redox reaction. In the present invention, it is particularly preferable to use a material whose potential does not vary depending on the oxygen gas partial pressure. Such a redox functional layer 5 may be, for example, an organic compound layer or a polymer layer capable of performing a quinone-hydroquinone type redox reaction, an organic compound layer or a polymer layer capable of performing an amine-7quinoid type redox reaction. Preferred examples include polymer layers. In addition, here, the quinone-hydroquinone type redox reaction, taking the case of a polymer as an example,
For example, it refers to the reaction represented by the following reaction formula. (In the formula, R ₁ and R ₂ represent, for example, a compound with an aromatic-containing structure.) In addition, the amine-quinoid type redox reaction is the same as the above-mentioned polymer, for example, as shown in the following reaction formula. refers to something expressed as (−N=R ₃ =) n ₁ N−+H ⁺ , +e ^- ――――――→ ←―――――― (−NH−R ₄ )−n ₁ NH− (in the formula, R ₃ , R ₄ represents, for example, a compound having an aromatic-containing structure.) Examples of compounds that can form the layer 5 having such a redox function include the following compounds (a) to (c). (In the formula, Ar is an aromatic nucleus, each R ₅ is a substituent, m ₂ is 1
or the effective valence number of Ar ₁ , n ₂ is 0 or Ar ₁
A hydroxy aromatic compound represented by (the effective valence number of -1). The aromatic nucleus of Ar ₁ may be a monocyclic nucleus such as a benzene nucleus, or a polycyclic nucleus such as an anthracene nucleus, pyrene nucleus, chrysene nucleus, perylene nucleus, coronene nucleus, etc. Not only a benzene bone core but also a heterocyclic bone core may be used. As the substituent R ₅ ,
Examples include alkyl groups such as methyl groups, aryl groups such as phenyl groups, and halogen atoms. Specifically, for example, dimethylphenol, phenol, hydroxypyridine, o- or m-pendyl alcohol, o-, m- or p-hydroxybenzaldehyde, o- or m-hydroxyacetophenone, o-, m-
or p-hydroxypropiophenone, o
-, m- or p-hydroxybenzophenone, o-, m- or p-carboxyphenol, diphenylphenol, 2-methyl-8-
Hydroxynoline, 5-hydroxy-1,4-
naphthoquinone, 4-(p-hydroxyphenyl)
2-butanone, 1,5-dihydroxy-1,
2,3,4-tetrahydronaphthalene, bisphenol A, salicylanilide, 5-hydroxyquinoline, 8-hydroxyquinoline, 1,8
-dihydroxyatraquinone, 5-hydroxy-1,4-naphthoquinone, and the like. (b) The following formula

[Formula] (In the formula, Ar ₂ is an aromatic nucleus, each R ₆ is a substituent, m ₃ is 1 to the effective valence number of Ar ₂ , and n ₃ is 0 to
An amino aromatic compound represented by (indicating the effective valence number of Ar ₂ -1). As the aromatic nucleus of Ar ₂ and the substituent R ₆ , the same ones as Ar ₁ and the substituent R ₅ in compound (a) are used, respectively. Specific examples of amino aromatic compounds include aniline, 1,2-diaminobenzene, aminopyrene, diaminopyrene, aminochrysene, diaminocrystalline, 1-aminophenanthrene, 9-aminophenanthrene, 9,10-diaminophene. Nanthrene, 1-aminoanthraquinone, p-phenoxyaniline, o-phenylenediamine, p-chloroaniline, 3,5-dichloroaniline, 2,4,6-trichloroaniline, N-methylaniline, N-phenyl -p-
Such as phenylenediamine. (c) 1,6-pyrenequinone, 1,2,5,8-tetrahydroxynarizarin, phenanthrenequinone, 1-aminoanthraquinone, purpurin, 1-amino-4-hydroxyanthraquinone, anthralfin, etc. Quinones. Among these compounds, 2,6-xylenol and 1-aminopyrene are particularly preferred. Furthermore, as a compound that can form the redox functional layer 5 according to the example, (d) poly(N-methylaniline) [Onuki, Matsuda,
Koyama, Journal of the Chemical Society of Japan, 1801-1809 (1984)], poly(2,6-dimethyl-1,4-phenylene ether), poly(o-phenylenediamine), poly(phenol), poly2,6 xylenol ;
Quinone-based vinyl polymer condensation compounds such as pyrazoquinone-based vinyl monomer polymers, isoalloxazine-based vinyl monomer polymers, etc.
Organic compounds containing compounds of (a) to (c), (a) to (c)
Examples include low-polymerization polymer compounds (oligomers) of the compounds described above, or those having the redox reactivity, such as those in which (a) to (c) are fixed to a polymer compound such as a polyvinyl compound or a polyamide compound. Among these, poly(2,6 xylenol) is particularly preferred. Note that in this specification, the term polymer includes both homopolymers and interpolymers such as copolymers. In order for the compound capable of forming the above redox functional layer 5 to be deposited on the surface of the conductive substrate 1,
Aminoaromatic compounds, hydroxyaromatic compounds, etc. can be directly polymerized on the substrate surface by electrolytic oxidative polymerization or electrolytic deposition, or they can be synthesized in advance by applying electron beam irradiation, light, heat, etc. A method in which the polymer layer is dissolved in a solvent and fixed to the substrate surface by dipping/coating and drying the solution, and a method in which the polymer layer is directly fixed to the substrate surface by chemical treatment, physical treatment, or irradiation treatment. can be taken. Among these methods, electrolytic oxidative polymerization is particularly preferred. The electrolytic oxidative polymerization method is carried out by electrolytically oxidatively polymerizing an amino aromatic compound, hydroxy aromatic compound, etc. in a solvent in the presence of a suitable supporting electrolyte to deposit a synthetic layer on the surface of a conductor. Examples of the solvent include acetonitrile, water, dimethylformamide, dimethyl sulfoxide, propylene carbonate, etc., and examples of the supporting electrolyte include sodium perchlorate, sodium perchlorate, disodium sulfate, phosphoric acid, boric acid, tetrafluoroborate, and the like. Suitable examples include potassium tetrafluorophosphate and quaternary ammonium salts. The polymer membrane layers deposited in this way are generally very dense and can prevent the permeation of oxygen even in thin layers. However, in order to be usable in the present invention, the redox functional layer 5 is not particularly limited as long as it has the redox reactivity, and it does not matter how dense the layer is. The thickness of the redox functional layer 5 is preferably 0.1 μm to 0.5 mm. If it is thinner than 0.1 μm, the effect of the present invention will not be sufficiently achieved, and if it is thicker than 0.5 mm, the resistance of the layer will become too high, which is not preferable in terms of measurement. Further, the redox functional layer 5 can be used by impregnating it with an electrolyte. Examples of the electrolyte include dipotassium hydrogen phosphate, sodium perchlorate, sulfuric acid, tetrafluoroborate, and tetraphenylborate. Among these, sodium perchlorate is particularly preferred. A convenient method for impregnating the redox functional layer 5 with an electrolyte is to deposit the redox functional layer 5 on a conductive substrate and then immerse it in an electrolyte solution. An electrode in which a conductive substrate 1 is coated with a redox functional layer 5 as described above (hereinafter referred to as a redox electrode)
The partition layer 6, which is further coated on the surface of the oxidation-reduction functional layer 5 and the bicarbonate ion selective layer 7, prevents the movement of substances constituting each layer, and prevents the movement of substances constituting each layer by contact with the bicarbonate ions. It has a function of transmitting the potential difference generated in the bicarbonate ion selective layer 7 and the bicarbonate ions to the redox functional layer 5. As a layer having such a function, a polymer layer containing an electrolyte solution or an aqueous solution is preferable, and a gel-like polymer layer is particularly preferable. These polymers include polyvinyl alcohol (hereinafter abbreviated as PVA), celluloses such as acetylcellulose,
Natural water-soluble polymers such as gelatin and agar, and semi-synthetic natural water-soluble polymers such as mannan and starch are preferred, and among these, PVA is particularly preferred. To cover the redox functional layer 5 with the partition layer 6,
For example, it contains PVA 10% aqueous solution or electrolyte.
Create a 10% PVA aqueous solution, fully immerse the redox electrode in this solution, pull it out, air dry it, and then heat it to 150°C.
The drying process is repeated to obtain a desired thickness. The thickness of PVA is 0.2μm to 0.8mm, especially 10μm
~0.6 mm is preferred. As the carbonate ion selective layer 7 further coated on the surface of the partition layer 6, there is used a layer in which a polymer compound supports a bicarbonate ion carrier material and, if necessary, an electrolyte salt.
As a hydrogen carbonate ion carrier substance, the following formula (In the formula, R ₁₁ , R ₁₂ , R ₁₃ are the same or different alkyl groups having 8 to 18 carbon atoms, R ₁₄ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X ^- is Cl ^- , Br ^- or OH ^- ); quaternary ammonium salt represented by the following formula: (In the formula, R ₁₅ represents a phenyl group, a hydrogen atom or a methyl group, R ₁₆ represents a hydrogen atom or a methyl group, and R ₁₇ represents a hydrogen atom, a methyl group or an octadecyl group); Furthermore, the following formula Examples include compounds represented by: Among these, quaternary ammonium salts are particularly preferred. Examples of electrolyte salts include sodium tetrakis(p-chlorophenyl)borate, potassium tetrakis(p-
chlorophenyl)borate and the following formula (R ₁₈ ) ₄ NBF ₄ (wherein R ₁₈ is an alkyl group, preferably having 2 carbon atoms)
to 6 alkyl groups). Among these, especially potassium tetrakis(p-chlorophenyl)borate (KTpClPB)
is preferred. In addition, for the layer material supporting the bicarbonate ion carrier substance, examples of polymer compounds include organic polymer compounds such as vinyl chloride resin, vinyl chloride-ethylene copolymer, polyester, polyacrylamide, polyurethane, and silicone resin. Inorganic polymer compounds can be mentioned. Among these, vinyl chloride is particularly preferred. The plasticizer used is preferably one that is difficult to dissolve, and examples of such plasticizers include dioctyl sebacate, dioctyl adipate, dioctyl maleate, di-n-octylphenyl phosnate, and the like. In particular, dioctyl sebacate (DOS), di(2) sebacate
-ethylhexyl) is preferred. Tetrahydrofuran (THF) is particularly preferred as the solvent.
To coat the bicarbonate ion selective layer 7, the redox electrode is repeatedly immersed in a solution of a polymer compound, a plasticizer, and an ion carrier substance dissolved in a solvent such as THF, pulled up, air-dried, and then dried. This can be obtained by adjusting the thickness to a predetermined value. The thickness of the bicarbonate ion selective layer 7 is 0.1 μm.
It is preferable that the thickness be 3 mm, particularly 0.1 mm to 1.0 mm. (Test Example) Regarding the bicarbonate ion sensor having the partition layer 6 between the redox functional layer 5 and the bicarbonate ion selective layer 7 prepared as described above, the bicarbonate ion sensor was used as the working electrode, and saturated sodium chloride was used as the working electrode. Using a calomel electrode (SSCE) as a reference electrode, 0.1m
The electromotive response was measured at 37°C when a 0.5M sodium hydrogen carbonate solution was titrated into a 0.5M sodium hydrogen carbonate solution and the concentration was varied. Next, the influence of selectivity on anions, ie, chloride, perchlorate, acetate, and nitrate ions, was investigated. In addition, the effect on the dissolved oxygen concentration in the solution was investigated by measuring the fluctuation of electromotive force over a period of 10 hours. The above results are shown in Tables 1 and 2.

【table】

[Table] From the above results, in Examples 1 to 3, the slope of the Nernst plot was the theoretical value of 61.55 mV/log.
It can be seen that the value agrees well with [HCO ₃ ^- ], and the slope of the Nernst plot hardly changes during the three months, indicating a stable value. Furthermore, it can be seen that there is substantially no elution of the substance constituting the redox functional layer into the bicarbonate ion selective layer, and there is substantially no elution of the substance constituting the bicarbonate ion selective layer into the redox functional layer. As confirmation methods, the absence of elution was confirmed using measurements of intensity changes in visible and ultraviolet spectrum absorption, liquid chromatography, and the like. Furthermore, it can be seen that the selectivity for chloride ions, perchlorate ions, acetate ions, and nitrate ions is good, and that there is no influence from dissolved oxygen. Also, the 95% response speed was within 1 minute. Note that this example is one example of the present invention, and the present invention is not limited thereto, and the composition of the constituent materials forming each layer is not limited thereto either. Effects of the Invention The present invention prevents mutual movement of substances constituting each layer between the redox functional layer and the bicarbonate ion-selective layer, and prevents the mutual movement of substances constituting each layer, and prevents the transfer of substances that occur in the bicarbonate ion-selective layer upon contact with bicarbonate ions. By providing a partition layer that has the function of transmitting a potential difference from the bicarbonate ion selective layer to the redox functional layer, mutual dissolution and elution of the redox functional layer composition and the ion selective layer composition, such as redox The quinoid compound (reddish brown) in the functional layer no longer elutes into the ion-selective layer, and the ionic properties, that is, the slope of the Nernst plot, do not change over a long period of time, and the selectivity is maintained even against the interference of anions. Excellent, fast ion response speed. In addition, since it is a solid-state sensor, different from a glass-type sensor that has a liquid chamber inside, it is easy to handle.
Since it is compact and difficult to break, it can be used as a medical sensor to measure the bicarbonate ion concentration in living organisms by combining it with guide wires, catheters, etc.
It can be used to monitor electrolyte balance in living organisms.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the bicarbonate ion sensor of the present invention. 1... Conductive substrate, 1a... Bottom surface of conductive substrate,
2...Lead wire, 3...Teflon coating, 4...
Heat shrink tube, 5... Redox functional layer, 6...
Partition layer, 7... Bicarbonate ion selective layer, 8...
Conductive adhesive, 9...insulator layer.

Claims (1)

[Claims] 1. In a bicarbonate ion sensor that includes an ion-sensing section and measures the ion concentration in a solution by electrode potential response, the ion-sensing section includes a conductive substrate;
comprising a redox functional layer covering the surface of the conductive substrate, a partition layer covering the surface of the redox functional layer, and a bicarbonate ion selective layer covering the surface of the partition layer,
The partition layer prevents the movement of substances constituting each layer between the bicarbonate ion selective layer and the redox functional layer, and prevents the potential difference generated in the bicarbonate ion selective layer upon contact with bicarbonate ions. 1. A hydrogen carbonate ion sensor, characterized in that it has a function of transmitting from a hydrogen carbonate ion selective layer to a redox functional layer.